Recursive variants

Is the purpose of Variant2 to only implement `std::variant` or to have new interfaces? Is this the right place to discuss the possibility of a shared/recursive variant? I don't have any statistics, but I think mixing shared_ptr and variants is a common pattern to have recursive variants? Could there be a shared_variant that takes some of the boilerplate away and adds more operations (e.g. shared_from_this, upcasts, ...)?

The issue contains no file, test, or entry point to start from; first read the Variant2 API and existing recursive-variant discussions. Done would require a maintainer decision on whether Variant2 should add new interfaces and whether a shared_variant belongs in this project.

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